(1) Field of the Invention
The present invention relates to network interconnection apparatus and method, and more particularly, to an apparatus and method for interconnecting a LAN (Local Area Network) and an ATM (Asynchronous Transfer Mode) network to perform communications.
(2) Description of the Related Art
ATM is a connection type communication mode developed so as to permit, within a single network, communications of multimedia information including data, voice, moving images, etc. to be performed at respective required rates while ensuring respective required qualities.
With conventional LANs which are preconditioned on broadcast function and connectionless type communication mode, it is difficult to ensure communication band or quality with respect to the requirements of such real-time communications of voice, moving images, etc. Attempts have therefore been made to construct LAN-ATM in which ATM is applied to LAN, and there is a need for economical and seamless connection between the two.
To permit interconnection of LAN and ATM, ATM Forum LAN Emulation (hereinafter abbreviated as LANE) Ver. 1.0, for example, is prescribed. LANE is a set of specifications that permit the connection and communications between an existing LAN environment and an ATM network environment, and emulation is carried out using the MAC (Media Access Control) layer of the LAN. Specifically, nodes are interconnected permanently by SVC (Switched Virtual Connection) at best-effort UBR (Unspecified Bit Rate) of the ATM network, to exchange data frames between the LAN and the ATM. Interconnection of LAN and ATM is also prescribed in LANE Ver. 2.0 and MPOA (Multi Protocol Over ATM) Ver. 1.0.
Meanwhile, with the advent of a multimedia network era, increasing attention has recently come to be directed to the QoS (Quality of Service) which networks provide. What is demanded from networks is, for example, up to at what degree of resolution and at what rate of transmission video can be sent to a destination.
Conventional techniques for guaranteeing QoS include a technique disclosed in Japanese Patent Application Laid-open Publication No. 9-331360, for example, in which call connection is tried first according to set QoS parameters, and if the call connection fails, the call connection request is repeatedly tried with the QoS request level gradually lowered until the call connection succeeds, to thereby guarantee QoS.
Concerning the guarantee of QoS, which is an advantage of ATM, LANE Versions 1.0 and 2.0 and MPOA Ver. 1.0 mentioned above have a problem in that they are not designed to guarantee QoS.
In LANE Ver. 1.0, for example, although ATM network is used to transfer LAN data through UBR connection, QoS is not guaranteed.
In the conventional technique disclosed in Japanese Patent Application Laid-open Publication No. 9-331360, on the other hand, QoS corresponding to physical port, destination address, application identifier, etc. is set beforehand, and accordingly, a problem arises in that the QoS guaranteed does not necessarily reflect actual traffic.
In addition, since the call connection request is repeated with the QoS level lowered until call is established, without regard to the status of network resources, there is a possibility of a large number of lost calls being generated, giving rise to a problem that useless traffic occurs in the network.